This project deals with the isolation and characterization of lymphocytes grown from endomyocardial biopsies from heart transplant patients. We have developed methodologies of growing activated lymphocytes from heart transplant biopsies. These cultured cells frequently exhibit alloreactivity towards donor histocompatibility antigens. Studies are proposed to analyze the allospecificity patterns of these lymphocytes and compare them with the allospecificity of lymphocytes derived from peripheral blood. This will be done in secondary proliferation assays using well-defined HLA-typed cell panels. Additional blocking studies will be performed with class I and class II specific monoclonal antibodies to verify the allospecificity of heart biopsy-grown lymphocytes. We are interested in extending our preliminary observations demonstrating that many biopsies yield alloreactive T lymphocytes with restricted allospecificity patterns. Particularly relevant are studies showing the class I specificity of lymphocytes grown from early biopsies. On the other hand, later biopsies primarily yield class II specific lymphocytes. Studies are proposed to evaluate the possible mechanisms of the sequential infiltration of different types of alloreactive T cells in the allograft. These studies will analyze the recognition of class I and class II HLA antigens on vascular endothelial cells by alloactivated T cells during the cardiac allograft response. An important aspect of this study is the relevance of the presence of various types of alloreactive T cells to the outcome of the transplant. Studies are proposed to evaluate a possible association between the presence of donor-specific cytolytic T cells and transplant rejection. Also, we are interested to know why it is possible to grow alloreactive T cells from transplant biopsies from patients with long-term transplant survival. Studies are designed to determine the presence of suppressor cells contributing to allograft tolerance. Experiments are also planned to determine whether lymphocytes from long-surviving transplants have greater sensitivity to immunosuppressive drugs than lymphocytes from rejecting transplants. These studies may provide valuable information about cell-mediated immune responses to cardiac transplants. Besides learning more about T cell allorecognition in the cardiac allograft response, this project may also generate data and concepts which could be clinically useful in the management of the heart transplant patient.